Storm Forecast
Valid: Wed 25 May 2016 06:00 to Thu 26 May 2016 06:00 UTC
Issued: Wed 25 May 2016 06:44
Forecaster: PUCIK

A level 1 was issued for E Poland, E Slovakia and NE Hungary mainly for excessive precipitation and to the lesser degree for marginally large hail.

SYNOPSIS

As a ridge stretches across the Norwegian Sea (associated with an extensive surface high over this part of the Atlantic), two separate lows are observed to the south. The first one resides over the Atlantic just to the west of Iberia. The second one, also quasistationary, will be centered over the W Black Sea. Jet-stream is observed on the southern flank of these features and in between of them, a ridge will begin to amplify northwards over the central Mediterranean.

Thunderstorm activity will be associated especially with the latter low, in a large belt spanning from Russia through E-central Europe towards the Balkans. Combination of uncapped environment and rather moist airmass will contribute to scattered tstm development as soon as the daytime heating ensues.
Lack of high CAPE / high shear environment will prevent very significant risk of severe weather, although some areas still require a closer inspection.


DISCUSSION

... Central France ...

Along and just south of the advancing warm front, GFS-based models continue to depict a development of several hundreds J/kg of CAPE despite the lack of steep lapse rates. This, in conjunction with an approach of stronger mid tropospheric flow and DLS above 20 m/s would point to a threat of isolated large hail with supercellular convection. However, current measurements show 6 - 10 deg C dewpoints over the region, while GFS predicts over 16 deg C for the afternoon hours. These values seem very unlikely to be realized. Furthermore, ECMWF is also much more skeptical regarding CAPE values. Due to the high uncertainty will refrain from issuing a Lvl 1 risk at the moment.

... E Poland, E Slovakia, NE Hungary ...

Storms will quickly develop in an uncapped environment in the prevailing northerly to northeasterly flow. With 10 - 15 m/s of DLS they will organise into multicells. The strongest storms may be capable of marginally large hail and excessive precipitation, the latter especially in case that training pattern develops with some of the multicells. Storm activity should quickly diminish after the sunset.